For more than 2000 years, people have observed that the leaves of the lotus flower are extremely water-repellant (superhydrophobic) and that, although the lotus grows in muddy water, the leaves never appear to be dirty. The advent of the scanning electron microscope in the 1970s enabled scientists to determine the properties of the lotus leaf that enable it to be self-cleaning: in addition to its waxy surface, the leaf contains microscopic bumps and hair-like structures that cause water to bead on the surface of the leaf rather than spreading out; the water droplets then roll down the leaf with little friction, removing dirt and bacteria along the way.
The discovery of the mechanism behind the “lotus effect” has led to interest in transferring this effect to artificial surfaces through a variety of patterning methods, resulting in surfaces that may clean themselves, for example, through a simple rainfall. Examples of the diverse markets that may benefit from development of cost-effective self-cleaning surfaces include automotive paint coatings, mirrors, and windows; and, alternative energy industries, such as solar cell arrays and wind turbine blades that benefit from being self-cleaning and/or easy to clean and maintain. However, present methods in this area are lacking in that they are time-consuming, expensive, ineffective, require highly specific, specialized, and expensive equipment, or require specialized laboratory environments to effectively implement.